Hello Frank ,
the idea and concept of the V 69 came from engineers and technicians from the "Abteilung Zentraltechnik" des NWDR ( Nord Westdeutscher Rundfunk ) and Telefunken only build this amp with F2a11 ( same as F2a , other socket ) and this tubes were only build bei Siemens . TFK had their EL 156 at this times ( which only came from TFK , no other manufacturers ) , their was no need for a further power tube . You can buy EL 156 with a Siemens logo , but they are TFK . I have never seen a F2a(11) with an other logo than Siemens ( and I have many of this tubes and also V 69 amps from TFK in their O 85 studio monitor ) .
Regards , AlexK .